Characterizing BPR Activity to Understand Overall Process Health

Factors affecting biological phosphorus removal (BPR) include operational conditions, influent characteristics, availability of volatile fatty acids (VFA), rainfall, and competition for substrate with denitrifiers or glycogen accumulating organisms (GAO). However, readily available data for evaluating process performance sis often limited to effluent phosphorus or sampling of the influent stream or mixed liquor, which is usually difficult or impossible to adequately use to predict process instabilities that lead to upsets. In an effort to better understand the causes of BPR instability and to predict conditions where it may happen, Clean Water Services (CWS) has been conducting extensive research and bench testing of phosphorus release and uptake. The results of this testing show that phosphorus uptake rates of sludge from the end of the aeration zone can be substantial, indicating excess storage products (i.e. polyhydroxyalkanoate) remaining in the sludge. These uptake rates appear to be mainly a factor of PHA content and abundance of phosphorus accumulating organisms (PAO) (i.e. total PAO fraction) in the sludge. Because the testing results correlate well with basin removal performance and VFA load, online measurements may be a useful tool in predicting process upsets and knowing when to shift VFA inventory.